This invention relates to a regenerator for regenerative combustion burner, particularly, to a regenerator for regenerative combustion burner which has a long operation life, a capability of stable and high yield heat recovery during an extended term, and a possibility of realizing a reduced pressure loss.
Now, referring to drawings, the regenerative combustion burner will be explained by an example where the regenerative combustion burners are installed in the heating furnace. FIG. 1 is a schematic sectional view of the heating furnace that the regenerative burners are installed. In FIG. 1, the numeral 1 denotes a heating furnace; the numerals 2a, 2b denote paired regenerative burners, respectively, wherein the paired burners are arranged on the furnace wall and face each other; and the numeral 3a, 3b denote a regenerator, respectively, wherein each regenerator is established at the regenerative burner 2a, or 2b. The regenerators 3a and 3b are preferably to have a large specific surface, and are generally made of plural honeycomb structure bodies. The numeral 4a and 4b denote a fuel shut-off valve respectively, and pressurized fuel is supplied from a fuel supply source which is not shown to burners 2a and 2b at a predetermined flow rate, while these valves have opened. The numeral 5a and 5b denote a combustion air valve respectively, and pressurized air is supplied from air supply source which is not shown to burners 2a and 2b at a predetermined flow rate, while these valves have opened. The numeral 6a and 6b denotes a flue gas valve respectively, and the flue gas (hereinafter, referred as xe2x80x9cfurnace internal gasxe2x80x9d) which has passed through the regenerator 3a and 3b is drawn at a predetermined flow rate by an exhaust blower which is not shown, and it is discharged to the atmosphere, while this valve has opened.
In FIG. 1, when, for example, one burner 2a is in the fired condition, the fuel shut-off valve 4a is opened in order to supply the fuel thereto. And, the combustion air valve 5a is opened and the flue gas valve 6a is closed in order to push the air into one regenerator 3a. The air which has passed through the regenerator 3a, by taking a heat from the regenerator, becomes high-temperature tempered air, and then, it is supplied to the burner 2a. 
At the same period, in the other burner 2b, both of the fuel shut-off valve 4b and the combustion air valve 5b are closed, and flue gas valve 6b has opened. The furnace internal gas is drawn from burner 2b, and it is exhausted by the exhaust blower, after it passes through the regenerator 3b so that its heat is stored to the regenerator 3.
In the case of regenerative combustion in the heating furnace 1 using above mentioned regenerative burner 2a and 2b, alternate combustion which alternately switches the combustion burner 2a and 2b every the fixed time is done.
When the combustion is changeover and the other burner 2b is in the fired condition, the combustion fuel shut-off valve 4b and combustion air valve 5b are opened together and the flue gas valve 6b is closed so as to supply the air to the other regenerator 3b. The air which passed through the regenerator 3b being in high-temperature absorbs heat from the regenerator 3b, and it becomes the high-temperature tempered air to be supplied to the burner 2b. 
In the meantime, in the burner 2a, the fuel shut-off valve 4a and combustion air valve 5a are closed together, and the flue gas valve 6a is opened, and thus the furnace internal gas is drawn from burner 2a, and it is exhausted by the exhaust blower, after it passes through the regenerator 3a so that its heat is stored to the regenerator 3a. 
At a separate pair of burners 2a1, 2b1, which are adjacent to the foregoing paired burners 2a, 2b, in the longitudinal direction of the furnace, a similar alternate combustion is done. However, the timing of the combustion is different. That is to say, when the burner 2a is in combustion, the adjacent burner 2a1 is in heat storage condition.
Generally, as a material of the regenerator, ceramics such as alumina and cordierites, etc. are used. The life of the regenerator is greatly changed by temperature of the flue gas and use environments such as the existence of the metal dust in the flue gas. When the choice of material for the regenerator is improper, therefore, fuse or cracking of regenerator may be happened and/or clogging of regenerator may be caused, which are followed by the drastically shortened lifetime of regenerator, and at worst led into the condition of inoperative due to the reduced heat-recovery and the heightened pressure loss.
Especially, in case of the alumina, that has the alumina purity of about 97% and the porosity of over 30% is usually used. Thus, in case that the high-temperature exhaust gas involves metal dust and being in amply high temperature, the fuse of regenerator can be happened by the reaction with the metal dust, and which is followed by the inoperative result. In addition, the life of the regenerator is greatly affected by alumina purity and porosity. Incidentally, the porosity showed the volume ratio of the pore in the material.
When comparing alumina with cordierite, the price of the alumina is generally higher than that of the cordierite. Further, as the purity goes up, and as the porosity goes down, the alumina tends to costlier.
The present invention, therefore, aims to provide a regenerator for the regenerative combustion burner capable of maintaining a stable heat recovery and low pressure loss in the long term, in keeping with low cost and by adopting an optimum construction, after clarifying the durability of alumina under a given alumina purity, given porosity, given atmosphere temperature and given condition for existence or nonexistence of the metal dust, or after clarifying the working condition of cordierite under a given atmosphere temperature and given condition for existence or nonexistence of the metal dust.
The first invention is characterized by the fact that, in a regenerator made of the materials each comprising alumina as a main ingredient, wherein the regenerator is used in a regenerative combustion burner being fired with alternately and repeatedly operations of heat storage by the passage of high-temperature flue gas in a fixed time and heating of combustion air by passage of the combustion air in a next fixed time; and the regenerator is used under the condition that the aforesaid flue gas includes metal dust;
the alumina purities in the materials for the regenerator are lowered in the order, the high-temperature, medium-temperature and low-temperature parts of the regenerator.
The second invention is characterized by decreasing the porosity of the aforesaid high temperature part in comparison with the porosity of the medium temperature part.
The third inventions is characterized by the fact that, in a regenerator made of the materials each comprising alumina as a main ingredient, wherein the regenerator is used in a regenerative combustion burner being fired with alternately and repeatedly operations of heat storage by the passage of high-temperature flue gas in a fixed time and heating of combustion air by passage of the combustion air in a next fixed time; and the regenerator is used under the condition that the aforesaid flue gas includes metal dust;
the alumina purity in the material for the high-temperature part of the regenerator where the flue gas is exceeding 1200xc2x0 C. is not less than 98%, that for the medium-temperature part of the regenerator where the flue gas is exceeding 1100xc2x0 C. and not higher than 1200xc2x0 C. is 95%, and the material for the low-temperature part of the regenerator where the flue gas is not higher than 1100xc2x0 C. is cordierite.
The fourth invention is characterized that the porosity in the high-temperature part is not more than 20%, and the porosity in the medium temperature part is not more than 50%.
The fifth inventions is characterized by the fact that, in a regenerator made of the materials each comprising alumina as a main ingredient, wherein the regenerator is used in a regenerative combustion burner being fired with alternately and repeatedly operations of heat storage by the passage of high-temperature flue gas in a fixed time and heating of combustion air by passage of the combustion air in a next fixed time; and the regenerator is used under the condition that the aforesaid flue gas does not include metal dust;
the alumina purity in the material for the high-temperature part of the regenerator where the flue gas is exceeding 1300xc2x0 C. is not less than 95%, and the material for the low-temperature part of the regenerator where the flue gas is not higher than 1300xc2x0 C. is cordierite.
The sixth invention is characterized that the porosity in the high-temperature part is not more than 20%.